138 W. D. Lambert — Mechanical Curiosities 



We may, if we like, consider that the floating continent 

 has fallen in moving toward the equator. In calculating 

 the difference of potential between one position and 

 another, we must take account of the mass of the liquid 

 displaced. 



All this is quite speculative of course ; it is based on the 

 hypothesis of floating continental masses and on the 

 assumption of a sustaining magma that would, of course, 

 be a viscous liquid, but viscous in the sense of the classical 

 theory of viscosity. According to the classical theory a 

 liquid, no matter how viscous, will give way before a 

 force, no matter how small, provided sufficient time be 

 allowed for the latter to act in. The peculiarities of the 

 field of force of gravity will give us minute forces, as we 

 have seen, and the geologists will doubtless allow us 

 aeons of time for the action of the forces, but the viscosity 

 of the liquid may be of a different nature from that postu- 

 lated by the classical theory, so that the force acting 

 might have to exceed a certain limiting amount before the 

 liquid would give way before it, no matter how long the 

 small force in question might act. The question of viscos- 

 ity is a troublesome one, for the classical theory does not 

 adequately explain observed facts^"^ and our present know- 

 ledge does not allow us to be very dogmatic. The equa- 

 torward force is present, but whether it has had in 

 geologic history an appreciable influence on the position 

 and configuration of our continents is a question for 

 geologists to determine. At any rate it may be consid- 

 ered as one of the mechanical curiosities with which 

 this paper deals. 



We do not, however, need to deal with hypothetical 

 rolling spheres or floating continents in order to find 

 room for the manifestation of peculiarities of the earth's 

 field of force. We can set up in the laboratory or in 

 the field a comparatively small instrument that will give 

 not merely qualitative evidence of these peculiarities but 

 accurate measurements of them. 



Let us consider a rod suspended at its middle by a deli- 

 cate fiber. The rod is loaded at both ends so that as 



"Jeffreys, The Viscosity of the Earth, Monthly Notices of the Eoyal 

 Astronomical Society, vol. 75 (1915), p. 648, and vol. 76 (1915), p. 84. 

 Michelson, The Laws of Elastico-Viscous Flow, Journal of Geology, vol. 25, 

 p. 405, 1917, and vol. 28, p. 18, 1920. 



